1. Field of the Invention
The invention relates generally to an electrode for arc furnaces, and particularly to a nipple configuration for a composite electrode comprising a liquid-cooled upper section and a graphite lower section joined to the upper section.
2. Previous Developments in the Art
The conventional material employed for the fabrication of electrodes for arc furnaces is graphite. These electrodes are consumed in use due to erosion and corrosion caused by oxidation, vaporization, spalling and other factors. This consumption involves tip losses, column breakage losses and particularly side oxidation losses. An average electric furnace consumes four to eight kilograms of graphite per ton of steel produced.
One method for reducing the consumption of graphite electrodes in arc furnaces has been the application of a protective coating or cladding material to the electrodes with oxidation resistant materials. However, due to the nature of graphite, formidable problems have been experienced regarding the wetting of the electrodes with such coatings, thereby rendering them somewhat ineffective for their stated purpose. Concerning claddings, the dissimilar thermal expansion and other properties of graphite and the cladding material tend to cause damage or slippage of the cladding and/or electrode.
Another known means for reducing graphite electrode consumption involves the utilization of fully non-consumable electrode systems. The systems employ full length liquid-cooled electrodes with selected apparatus to protect the electrode tip from the extreme temperatures of the arc. Although such systems appear in the patent literature, this design has not been commercially successful.
It has been suggested heretofore that composite electrodes comprising carbon or graphite portions attached to a water-cooled upper piece would provide means for reducing electrode consumption in arc furnaces. A number of patents have issued on specific composite electrode designs. For example, U.S. Pat. Nos. 2,471,531 to McIntyre et al,; 3,392,227 to Ostberg; 4,121,042 and 4,168,392 to Prenn; 4,189,617 and 4,256,918 to Schwabe et al.; 4,287,381 to Montgomery and 4,416,014, 4,417,344 and 4,451,926 to Hogg et al. relate to liquid cooled composite electrodes for arc furnaces. Likewise, European patent application Nos. by C. Conradty Nurnberg designated 50,682, 50,683 and 53,200 and 77,513 by Von Roll AG are directed to composite electrode configurations.